Historic port of interpianac from the NeXt Max version. interpianac is doing an interpolation between partial frames right after a iana~ analysis. The interpolation is done with frequencies that are the closest and not their index.
Instead, I would now advice you to use the threefates external from CNMAT depot.
Ircam Max version 0.26 audio test patch on NeXTSTEP before a playing a piece. One can see the squares on the top left of the window showing the six CPUs for DSP.